# Polyurethane

## Hazards

Avoid contact with the liquid and vapor of the chemicals in this demonstration.

## Chemicals and Solutions

• 100 ml of polyurethane a (toluene diisocyanate plus extras)
• 136 ml of polyurethane b (gycerol plus extras)

## Materials

• large plastic beaker (2 L capacity)
• stirring rod

## Procedure

Mix components a and b in the beaker. Stir until the mixture starts to foam.

## Discussion

The polyurethane forms when an isocyanate group (R-N=C=O) from toluene diisocyante reacts with a hydroxyl group from glycerol forming an ester-like bond. The reaction can proceed in three directions since all three hydoxyl groups of the triol can react and both isocyanate groups can react.This leads to a large molecule that is rigidly held into a three dimensional structure.

The foaming is caused by the small amount of water that is present. The water decomposes isocyanate:

$$\ce{ R-N=C=O + H2O -> RNH2 + CO2 }$$